State -> StateFile

src/state_file.rs

@@ -0,0 +1,59 @@
+use anyhow::{bail, Context, Result};
+use serde::{Deserialize, Serialize};
+use std::fs;
+
+use crate::exercise::Exercise;
+
+#[derive(Serialize, Deserialize)]
+pub struct StateFile {
+    next_exercise_ind: usize,
+    progress: Vec<bool>,
+}
+
+impl StateFile {
+    fn read(exercises: &[Exercise]) -> Option<Self> {
+        let file_content = fs::read(".rustlings.json").ok()?;
+
+        let slf: Self = serde_json::de::from_slice(&file_content).ok()?;
+
+        if slf.progress.len() != exercises.len() || slf.next_exercise_ind >= exercises.len() {
+            return None;
+        }
+
+        Some(slf)
+    }
+
+    pub fn read_or_default(exercises: &[Exercise]) -> Self {
+        Self::read(exercises).unwrap_or_else(|| Self {
+            next_exercise_ind: 0,
+            progress: vec![false; exercises.len()],
+        })
+    }
+
+    fn write(&self) -> Result<()> {
+        // TODO: Capacity
+        let mut buf = Vec::with_capacity(1024);
+        serde_json::ser::to_writer(&mut buf, self).context("Failed to serialize the state")?;
+
+        Ok(())
+    }
+
+    #[inline]
+    pub fn next_exercise_ind(&self) -> usize {
+        self.next_exercise_ind
+    }
+
+    pub fn set_next_exercise_ind(&mut self, ind: usize) -> Result<()> {
+        if ind >= self.progress.len() {
+            bail!("The next exercise index is higher than the number of exercises");
+        }
+
+        self.next_exercise_ind = ind;
+        self.write()
+    }
+
+    #[inline]
+    pub fn progress(&self) -> &[bool] {
+        &self.progress
+    }
+}